1. Field of the Invention
This invention relates to coupling devices adapted for use in submarine oil and gas wells, and particularly, for detachably interconnecting sections of casing at a location below the floor of the sea or ocean.
2. Brief Description of the Prior Art
It has been generally recognized in the technology of oil and gas exploration and production, that in some contexts, it is desirable to provide a safety coupling or a releasable joint which can be used for selectively disconnecting the upper portion of a tubing or casing string from a lower portion thereof. Often, in off-shore completions, it is desirable to remove the well head and sections of casing thereabove from the sections of casing below the well head, and particularly below the ocean floor, in order to cement in the well and leave the sea floor clean at the situs of the closed in well after operations are completed.
In general, it is recognized that couplings or joints which are severable or disengagable by actuation from the surface afford advantage where the disengagement can be effected without imparting a rotary motion to the actuating mechanisms within the joint or coupling. Rather, it is preferred to be able to effect the disconnection by an axial, up or down movement, or by application of a force without the requirement for such rotary motion.
A number of different types of safety joints or detachable couplings have previously been proposed, and in many instances include movable collars or sleeves temporarily secured in position by a shear pin, and used in conjunction with other structural elements or mechanisms for effecting firm coupling and engagement between casing sections during the operative employment of the casing sections for transmitting fluids between the bottom of the well bore and the surface, but actuatable at a time when it may be desired, for one reason or another, to detach the upper section of the casing from the lower section, and remove it from the well bore. The various structures which have been provided for accomplishing the prescribed functions have been numerous, and operate on different principles. Frequently the mechanisms which must be actuated and function properly, in order to allow safe, rapid and economical severence or disconnection of the casing sections to be effected, are complicated and, because of such complexity, are characterized in having a relatively high susceptibility to failure or malfunction. Also, many of the types of coupling structures provided for the described purpose have not afforded protection of the moving elements from contact with fluids flowing internally in the casing or tubing string, or from contact with deleterious external fluids, such as percolating sea water or the like.
Other problems, or lack of optimization, have been characteristic of many of the various other types of couplings utilized for interconnecting, on a temporary basis, vertically aligned casing sections. In some instances, such as the mechanism shown in British Pat. No. 999,838, actuation of the coupling mechanism to effect disconnection must be brought about by the use of hydraulic pressure developed form the surface to actuate a piston which moves to effect the disengaging action. In other types of joints or couplings previously proposed, a portion of the actuating mechanism is left in the well upon disconnection of the casing sections, thus presenting an economic loss, and the necessity to reconstitute or re-make up the safety joint structure if any attempt is made to subsequently use it in another well installation. Examples of prior art devices which leave portions of the operating mechanism in the well with the lower portion of the severed casing are described in Brown U.S. Pat. No. 3,288,493; Arterbury et al U.S. Pat. No. 2,843,399 and Schwabb U.S. Pat. No. 3,148,894. The same is true of the mechanism as shown in Ware U.S. Pat. No. 2,532,686. The previously mentioned disadvantage of exposure of operating or moving parts of the disconnection mechanism to well fluids moving within the bore through the casing, or to external fluids, such as sea water, outside the casing, is also characteristic of the Schwabb and Brown Patents. Such exposure is also characteristic of the coupling disconnecting mechanism shown in Clark U.S. Pat. No. 2,988,145.
It is also often a disadvantage of the disconnect mechanisms employed in severable joints or couplings of the type described that an initially downwardly acting force must be developed on the mechanism prior to the lifting or pulling out of the upper casing section following the disconnection of the coupling. In other words, two opposite acting forces developed at different times must be provided in order to effect the disconnection and removal of the upper casing section. This type of dual action is characteristic of the structures described in the Brown and Schwabb Patents.
In general, although the types of coupling safety joint structures provided for temporarily and operatively engaging axially aligned upper and lower casing or tubing sections have been operational and functioned properly and effectively upon the first usage, and if manipulated by skilled operators, none of the devices known to the prior art have been characterized by optimum simplicity of structure, and a high degree of reliability in use over long and extended periods.